Original subtitles

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So now that you've learned all about if, elif and else,

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as well as nested if statements,

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then I've got two code challenges coming up for you. In the first one, in the

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code challenge that's called day 3.2 BMI calculator

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2.0,

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this is going to be an upgraded version of the BMI calculator that you created

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yesterday.

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Instead of just working out the BMI value of somebody,

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we're going to give them an interpretation.

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You might've come across a BMI chart that looks like this,

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where it divides up people's BMI and tells them whether if the underweight,

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normal weight, overweight, et cetera. And this depends on the value of the BMI.

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So if the value of the BMI is less than 18.5,

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then they are underweight. If they're over 18.5,

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but below 25, then they have a normal weight.

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So your job is to not only create a BMI calculator,

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but also to give them the corresponding interpretation message.

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Now it's really,

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really important that you use the words here that are highlighted in bold in your

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interpretation, that based on a particular height and weight,

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you actually give them the correct interpretation.

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Pause the video and try to give this challenge a go.

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All right. So how did you get on?

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There was a little bit of a revision from what you've done previously.

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Hopefully you've been able to calculate the BMI without much trouble and then

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use what you learned about if, elif and else to provide the user with the

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corresponding interpretation for the BMI that they have.

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Let's start out by calculating the BMI. And the BMI,

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according to this equation is equal to the weight in kilograms

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divided by the height squared. So we've got the weight already,

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and then we divided by the height to the power of two.

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Now, notice how I've already converted these inputs to floats.

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So we don't have to do what we did previously when we were calculating the BMI.

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Now what the exercise does mention though

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is that we should round the result of the nearest whole number.

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But you probably remember how to do this right? Using the round function.

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So if we wrap the entire equation inside a round function,

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then it's going to round it to the nearest whole number.

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So if this is what you got stuck on, then head back to your code and just fix it.

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Now, once we've calculated the rounded value of BMI,

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the next step is to give the user an interpretation message based on their BMI.

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So let's start with the first one.

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If the BMI is less than 18.5,

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well then in this case, they're actually underweight, right?

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So it will print something like your BMI is,

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and then inside here we'll insert the value of their BMI.

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And this of course is using f-strings, so let's add an F to the beginning.

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Your BMI is this particular value and you are underweight.

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Now,

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what if their BMI was between 18.5 and 25?

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Well, because we've already checked that their BMI is less than 18.5,

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then if this is false because it's jumped to the next level,

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then we don't actually have to check this.

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All we have to do is check that it's still below 25. And to do that,

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we're going to use an Elif.

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So elif BMI is less than 25, well then in this case,

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we're going to print you bmi

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is this particular value, and you have a normal

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weight. If this is a little bit mysterious to you,

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why it is that I'm not checking that their BMI is over 18.5,

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but below 25 and I'm simply just checking that it's less than 25,

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then I recommend having a play around with the code as it is right now,

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and trying out some different values for BMI.

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Just change this to say 18,

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and then try maybe something like 22 so that it's caught by each of these

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conditions. And then you'll soon realize that this

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if, elif, else is an entire group of statements,

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and it's going to check this one first and only if this fails,

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when it's false, does it go and check the next one.

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So then this is only going to be printed when their BMI is over 18.5,

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but below 25. And once you're comfortable with this,

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then the rest of the statements should be pretty easy.

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All right,

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Now,

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once we've reached here and their BMI is not less than 35 and we want to catch the

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remaining cases where the BMI is over 35,

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then all we have to do is add an else statement.

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That's all we have to do.

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We've managed to check for those people that have BMI less than 18.5.

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If it's not less 18.5, well, is it less than 25?

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So this will print when the BMI is greater than 18.5,

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but less than 25. And we've done that for all of these separate statements.

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If you struggled with this code,

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then I recommend having a look back at the previous lesson where we talked more

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in detail in terms of if, elif and else.

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If you struggled with this challenge,

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then have a go at pasting the code that's in the solution into the Thonny code

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editor. And instead of having the BMI being a workout value,

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just set it to some different numbers. So for example, if we start out testing,

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if the BMI is equal to 18,

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which of these will it fall into, then we can click on the debug step into each

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of these. And you can see that when it evaluates this condition,

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is the BMI less than 18.5, well,

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18 is less than 18.5. So this is true.

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And in that case, it's going to execute this line of code.

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So it is going to print out your BMI is 18, you are underweight.

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And then it's done. That's the end of the code. Now,

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if we change this to say 22 however, and we click on debug,

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then it's going to evaluate the first condition, is 22 less than 18.5 and

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that's going to be false.

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So then it skips to the next elif that it can find

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and it checks whether if the BMI 22 is less than 25.

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So now it's going to execute this print statements.

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Have a play around with that

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if it's still a little bit mysterious to you and hopefully,

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once you're done there,

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then you'll be ready to move on to the next code challenge

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which is a little bit more challenging. For all of that and more,

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I'll see you there.